So far, installation of valves in the pipeline simultaneously with the laying of the pipeline has been difficult. This is mainly due to the weight and rigidity of the valves. An actuator is often mounted on top of the valves, and the installation of the valves on the seabed must therefore be closely monitored. The actuator on the valve housing cover cannot deviate many degrees from straight upright position before the function becomes problematic. These difficulties have in many cases contributed to the installation of the valve on the pipeline after the latter is installed on the seabed. The installation of the valve can take place by cutting off a piece of the pipeline and welding the valve into the resulting space.
Another procedure for the laying of pipelines consists of the insertion of a blind tube where a valve is desired to be mounted. This blind tube acts as a temporary joint to the other parts of the pipeline and must be of the same length as the valve to be inserted.
A known emergency shut-down valve will for a 20" pipeline have a length of approx. 6 meters and a weight of approx. 50-80 tons. Inspection, control and maintenance of such a valve must take place at certain intervals, and the inspection etc. will be endeavored to be executed without interruption of the production. A known method for implementation of this is that an internally displaceable telescopic tube is mounted in the valve housing area and is moved to isolate the valve housing from the pipeline. Thus, the valve chamber with check valve is shut off from the production pipe. Thereafter, the housing cover with check valve and actuator can be dismantled for inspection. Such an operation requires that the housing cover can be relatively easily and quickly released from the valve housing flange.
Mounting and possible dismantling must be feasible at great depths. It is therefore important that this work can be implemented in an easy, simple and quick way with a minimum risk of damage.
The state of the prior art moreover comprises U.S. Pat. Nos. 1,841,882 issued Jan. 19, 1932; 2,575,667 issued Nov. 20, 1951; 3,647,108 issued Mar. 7, 1972; and German Patent No. 1,245,235 issued July 20, 1967.
U.S. Pat. No. 1,841,882 relates to a hydraulic motor where the motor cylinder has a head or cover screwed on, designed with four locking segments similarly spaced around the circumference. Each of these locking segments are U-shaped where the facing contact and sealing surfaces are not parallel, but form an acute angle with each other. The engagement between an outward facing flange on the motor cylinder and the lock segments is determined by the shape and takes place under prestressing of the locking segments. Such a locking device is therefore not very appropriate for clamping and locking of a cover to a valve housing on subsea pipelines at great depths, where simple installation is required without pressure or great pre-stressing forces.
U.S. Pat. No. 2,575,667 relates to a pressure-resistant heating vessel where the cover is clamped and locked to a flange on the container by means of a number of locking segments similarly spaced around the periphery with curved opposite facing sealing surfaces. Also here, the clamping/locking is determined by the shape and takes place under engagement between interacting parts and pre-stressing of the locking segments. This locking device, too, is inappropriate for the purpose concerned, where pre-stressing of the locking segments should be avoided to the greatest possible extent.
U.S. Pat. No. 3,647,108 relates to a closure for pressure vessels, including a resilient seal ring having an outer lip and an inward by turned flange angularly disposed to the outer lip, whereby pressure within the vessel is exerted through an opening in the seal ring to urge this into a position where it forms a sealing relation with the vessel around an opening in the vessel. The closure member contains a dent for accommodation of the sealing ring and a number of anchoring elements in the dent, where the anchoring elements have surfaces for engagement with slip-rings to press the slip-rings to engaging contact with a portion of the vessel. Moreover, it should be clear that such a locking device with resilient seal ring is entirely inadequate at great depths.
German Pat. No. 1,245,235 relates to a safety device for shutters or covers for pressure vessels, where locking is determined by the shape and takes place under engagement and pre-stressing of locking elements similarly spaced around the shutter/cover circumference. Also this well-known device suffers from the disadvantages and deficiencies emphasized in connection with the abovementioned locking devices.